yaml playout skip items expression (#2092)

CHANGELOG.md

@@ -46,6 +46,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   - The current time (as a decimal) can also be used in the expression, e.g. `now > 23`
     - `now = hours + minutes / 60.0 + seconds / 3600.0`
     - So `10:30 AM` would be `10.5`, `10:45 PM` would be `22.75`, etc
+- YAML playout: make `skip_items` an expression
+  - The following parameters can be used:
+    - `count`: the total number of items in the content
+    - `random`: a random number between zero and (count - 1)
+  - For example:
+    - `count / 2` will start in the middle of the content
+    - `random` will start at a random point in the content
+    - `2` (similar to before this change) will skip the first two items in the content
 
 ### Changed
 - Allow `Other Video` libraries and `Image` libraries to use the same folders

ErsatzTV.Core/Scheduling/YamlScheduling/Handlers/YamlPlayoutSkipItemsHandler.cs

@@ -20,12 +20,6 @@ public class YamlPlayoutSkipItemsHandler(EnumeratorCache enumeratorCache) : IYam
             return false;
         }
 
-        if (skipItems.SkipItems < 0)
-        {
-            logger.LogWarning("Unable to skip invalid number: {Skip}", skipItems.SkipItems);
-            return false;
-        }
-
         Option<IMediaCollectionEnumerator> maybeEnumerator = await enumeratorCache.GetCachedEnumeratorForContent(
             context,
             skipItems.Content,
@@ -33,7 +27,34 @@ public class YamlPlayoutSkipItemsHandler(EnumeratorCache enumeratorCache) : IYam
 
         foreach (IMediaCollectionEnumerator enumerator in maybeEnumerator)
         {
-            for (var i = 0; i < skipItems.SkipItems; i++)
+            var expression = new NCalc.Expression(skipItems.SkipItems);
+            expression.EvaluateParameter += (name, e) =>
+            {
+                e.Result = name switch
+                {
+                    "count" => enumerator.Count,
+                    "random" => new Random().Next() % enumerator.Count,
+                    _ => e.Result
+                };
+            };
+
+            object expressionResult = expression.Evaluate();
+            int skipCount = expressionResult switch
+            {
+                double doubleResult => (int)Math.Floor(doubleResult),
+                int intResult => intResult,
+                _ => 0
+            };
+
+            skipCount %= enumerator.Count;
+
+            if (skipCount < 0)
+            {
+                logger.LogWarning("Unable to skip invalid number: {Skip}", skipItems.SkipItems);
+                return false;
+            }
+
+            for (var i = 0; i < skipCount; i++)
             {
                 enumerator.MoveNext();
             }

ErsatzTV.Core/Scheduling/YamlScheduling/Models/YamlPlayoutSkipItemsInstruction.cs

@@ -5,5 +5,5 @@ namespace ErsatzTV.Core.Scheduling.YamlScheduling.Models;
 public class YamlPlayoutSkipItemsInstruction : YamlPlayoutInstruction
 {
     [YamlMember(Alias = "skip_items", ApplyNamingConventions = false)]
-    public int SkipItems { get; set; }
+    public string SkipItems { get; set; }
 }